Onstraints on timing of the early-Paleoproterozoic magmatism and crustal evolution of the Oulongbuluke microcontinent: U-Pb and Lu-Hf isotope systematics of zircons from Mohe granitic pluton.

The Olongbuluke micro-continent is composed of a two-fold basement with cover strata. The lower basement is the medium-to high-grade Delingha complex ( DC) and the Dakendaban Group, the upper is the low-grade Wandonggou Group. Zircon LA-ICP-MS dating gives U-Pb isotope of 27 zircon grains from the Mobe granite of the DC, of which 26 zircon grains suffered various degree of Pb loss and defined a Concordia with a upper intercept age of 2470 +19/- 18Ma. Hf isotope of 25 zircon grains was measured using LA-MC-ICP-MS technique, of which 23 grains crystallized from Mohe granite show Hf-i = 0.28129 similar to 0.28140 (weighted average of 0.28134 +/- 0.00003), epsilon(Hf) = 2.94 similar to 6.95 (weighted average of 4.58 +0.54/-0.76), resident time for the felsic crustal reservoir T-DM(C) = 2.54 similar to 2.75Ga with weighted average of 2.66 +0.04/-0.02Ga. These data indicate that the Mohe granite pluton was derived from, partial melting of the mantle, and the intrusion of the Mohe granite pluton implied a crustal accretion event occurred in Olongbuluke micro-continent at ca. 2.5Ga.